<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<style>
  div{
    width: 50vw;
    height: 50vw;
    background-color: red;

  }
</style>
<body>
  <div>消息</div>
</body>
</html>